GB2390881A

GB2390881A - A brake assembly using self energization

Info

Publication number: GB2390881A
Application number: GB0309697A
Authority: GB
Inventors: Dale Lee Hartsock
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2002-05-06
Filing date: 2003-04-29
Publication date: 2004-01-21
Anticipated expiration: 2023-04-29
Also published as: US20030205438A1; DE10320335A1; DE10320335B4; US6938737B2; US6752247B2; GB0309697D0; US20040178027A1; GB2390881B

Abstract

A brake assembly 10 for braking a selectively movable assembly (for eg., a motor vehicle), the brake assembly 10 having at least one movable self energization member 24, 26 (a wedge in this case) and a controller assembly 30, 34 coupled to the or each movable self energization members 24, 26 and which is operable to provide a controllable varying amount of self energization. The assembly may comprise a pair of movable self energization members 24, 26 which may each have a respective unique angle of inclination, and may be coupled to the controller assembly 30, 34 to provide the controlled amount of self energization. The assembly may comprise an accelerometer (not shown) which provides signals to the controller assembly 30, 34 so as to adjust the amount of self energization. There also exists an independent claim regarding a method for braking wherein a wedge coupling is provided.

Description

2 %q088 1 - 1 A Brake Assembly and a Method of Braking a Vehicle The

present invention generally relates to a brake assembly and method and in particular to a vehicular brake 5 assembly which provides a controllably varying amount of self energisation and to a method for operating such an assembly. An electromechanical braking assembly typically JO provides braking of a selectively movable assembly (such as a vehicle) by the use of a motor which becomes selectively energized upon a sensed depression of a brake member. At the outset, it should be appreciated that the term "selectively movable assembly" refers to any assembly, including but not limited to a vehicle, which has at least one component which may be selectively rotated and which must be selectively braked. Hence, it should be realized that the present invention 20 is applicable to a wide variety of such selectively movable assemblies and is not limited only to a vehicle. Further, while the terms "vehicle" and "selectively movable assembly" may be interchangeably used in this description, the present

invention is not limited to a vehicle or any other 25 particular type of selectively movable assembly.

Particularly, such an electromechanical braking assembly typically includes a rotor which moves with the wheel of the vehicle or other selectively movable assembly 30 in which the electromechanical braking assembly is operatively disposed and a pad which is made to engage the rotor, by the selectively activated motor, effective to brake the moving wheel and thereby brake the selectively movable assembly. Importantly, such an electromechanical 35 braking assembly does provide some advantages over traditional hydraulic brake systems.

f - 2 - One non-limiting example of such an electromechanical brake assembly is described in European Patent Number EP 0953785A3 which is fully and completely incorporated herein by reference, word for word and paragraph for paragraph.

By way of example and without limitation, such an electromechanical braking system provides the desired braking in a substantially shorter amount of time than that which is provided by a conventional hydraulic braking system 10 and allows each of the individual wheels of a vehicle or other selectively movable assembly to be selectively controlled, thereby enhancing the effectiveness of many operating strategies such as an anti-skid or anti-lock braking strategy or a strategy which is commonly referred to 5 as an "integrated vehicular dynamic" strategy.

However, while such an electromechanical braking system provides these and other advantages, it requires a relatively large motor which increases the overall cost of 20 producing the vehicle (or other selectively movable assembly) while concomitantly and undesirably requiring a relatively large packaging space which may require a modification in the packaging design of many assemblies, such as vehicle assemblies, which have respectfully and 25 relatively "tight" space constraints or requirements.

Further, the relatively large motor requires a relatively large amount of electrical power in order to operate, thereby requiring a relatively large battery or 30 power source, in excess of that which is conventionally placed within a vehicle, thereby further and undesirably increasing the overall production cost of the vehicle or other selectively movable assembly.

35 Further, current electromechanical brake systems utilize only a single motor and this architecture may be undesirable since these systems may not provide a desired

( - 3 amount of braking in the event that the single provided motor is not activated. In contrast to the "single motor" electromechanical braking system, an e'ectro-hydraulic braking system normally utilizes a manual second or "back up" braking assembly which brakes the vehicle or other selectively movable assembly in the event of that desired braking is not provided by the "primary" electro-hydraulic braking assembly. Although this approach does provide the desired redundancy, it undesirably increases the cost of 0 producing the vehicle, undesirably increases the amount of required packaging space, and, as earlier delineated, does not provide all of the features and benefits associated with an electromechanical braking system.

One attempt to overcome these drawbacks requires the use of a selfenergisation member having at least one or more substantially identical wedges which are deployed upon or provided by a single wedge member, and which is typically deployed within the electromechanical braking system.

20 Particularly, the at least one wedge (as well as the other wedges) has a fixed angle of inclination that provides additional mechanical advantage and assists in "forcing" the brake pad against the rotor, thereby reducing the amount of braking actuation power which must be provided by the motor.

2s Importantly, it is the shape or geometric configuration of the at least one wedge which assists the motor in braking the assembly, thereby conserving energy (e.g., the physical or mechanical properties of the at least one wedge provide 30 this desired "brake enhancing" functionality without requiring additional activation energy or power from the motor). Hence, a member which "provides" such a wedge is referred to as a "selfenergisation" member. While this approach does reduce the overall power requirements and the 35 size of the motor, it too has several drawbacks.

( - 4 For example and without limitation, a conventional electromechanical self-energizing braking system provides a fixed amount of self-energisation(an amount which is not selectively variable by a controlled amount and which is 5 wholly determined by the fixed angle of inclination of the at least one wedge as the selectively movable assembly moves in a certain direction), even though the amount of friction between the rotor and the pad varies with temperature, humidity, and other environmental conditions. Therefore, lo this arrangement requires the operator of the selective moving assembly to vary the amount of pressure or force which is exerted on the braking member in order to achieve the same amount of braking as these environmental conditions change during the operation of the selectively movable 15 assembly, thereby undesirably causing the operator to have an inconsistent braking "feel". Further, this approach does not allow for the use of a relatively low powered motor since the motor must be capable of operating under conditions in which the amount of friction between the rotor 20 and the pad is relatively high and when the amount of friction between the rotor and the pad is relatively low.

The inability of the motor to operate under these extreme frictional conditions might cause the brake assembly 25 to undesirably enter a tension mode (e.g., a mode in which the motor must overcome the friction force which is pulling the pad in the same direction as the rotor is moving in order to reduce braking force) from a desired compression mode (e.g., a mode in which the motor pushes the pad in the 30 same direction as the rotor is moving in order to generate a brake force).

That is, during a compression mode of operation which occurs when the frictional force is relatively low, an 3s "undersized motor" (e.g., a motor which does not provide enough actuation force to ensure desired operation in high and low friction conditions) may not be capable of

( generating the deceleration desired by the operator. During a tension mode of operation, which occurs when the frictional force is relatively high, an "undersized motor" may not be able to pull the pad with enough force to prevent 5 it from being frictionally "locked" onto the rotor, thereby preventing the braking assembly from providing the desired braking required by the operator.

Further, while the current electromechanical braking JO configuration, in the desired compression mode, provides a high gain at one level of friction (e.g., during high friction), it will provide a much lower gain at lower friction levels. This means that a larger actuating motor must be utilized than would be necessary if the wedge angle or the angle of inclination could be "optimized" (i.e., dynamically configured to provide large amounts of brake enhancement at each friction level). Hence, due to the use of a fixed amount of self-energisation (emanating from the use of a fixed angle of inclination), a relatively large 20 motor must be employed to ensure that the braking assembly functions during "worst case" situations in which a large amount of activation power is required.

Moreover, yet additional drawbacks exist if a single 25 and relatively small motor were utilized in a conventional electromechanical braking system which is designed to operate in both the compression mode and the tension mode.

That is, the relatively small motor must overcome the inertia associated with existing compression braking in 30 order to provide tension type braking, thereby resulting in a relatively slow response time which provides an uncomfortable "feel" to the operator of the selectively movable assembly. Moreover, the braking assembly, in overcoming such inertia, may even provide an undesirable 35 amount of compression or tension type force. In fact, at one instant of time, during this transition, the motor neither

! - 6 - provides compression nor tension and at this "zero point", the braking assembly may not function in a desired manner.

It is an object of the invention to provide an improved 5 brake assembly.

According to a first aspect of the invention there is provided a brake assembly for braking a selectively moveable assembly the brake assembly having at least one movable self lo energisation member and a controller assembly coupled to the or each movable self energisation member and which is operable to provide a controllable varying amount of self energisation. The selectively moveable assembly may be a rotatable shaft or may be a wheel of a motor vehicle.

According to one embodiment of the invention there may be a pair of movable self energisation members each of which 20 has a respective unique angle of inclination and the controller assembly is coupled to the pair of selectively movable members and arranged to cause the pair of movable self energisation members to cooperative so as to provide a controllable varying amount of self energisation.

The brake assembly may further comprise an accelerometer which is coupled to the controller assembly and which generates a certain signal which is transmitted to the controller assembly and which causes the controller 30 assembly to move at least one of the pair of selectively movable members by a certain amount.

Each of the movable self energisation members may have at least one wedge portion.

3s A first of the pair of selectively movable members may have a wedge portion which is dissimilar from a wedge

( - 7 portion of a second of the pair of selectively movable members. The controller assembly may comprise an electronic 5 controller which is operable under stored program control, a first motor which selectively moves one of the pair of self energisation members and which is coupled to the electronic controller and a second motor which selectively moves a second of the pair of self energisation members and which is 0 coupled to the electronic controller.

The first and second motors may be substantially i identical. 15 A wedge portion of the first of the pair of self energisation members may frictionally and slidably engage with a wedge portion of a second of the pair of self energisation members.

20 A brake pad may be coupled to a first one of the pair of self energisation members.

According to a further embodiment according to the first aspect of the invention there is one self energisation 25 member and the controller assembly comprises a brake pad for frictional engagement with a movable rotor, a backing plate which is coupled to the brake pad, at least one roller which is coupled to the backing plate, a caliper having at least one roller coupled thereto wherein the self energisation 30 member is a wedge member positioned between the or each roller coupled to the backing plate and the or each roller coupled to the caliper and is coupled to a motor used to selectively move the wedge member so as to brake a selectively movable assembly.

The selectively moveable assembly may be a wheel of a motor vehicle or may be a rotatable shaft.

( - The or each roller coupled to the caliper may orthogonally project therefrom.

The or each roller coupled to the backing plate may s orthogonally project therefrom.

Each roller coupled to the caliper may be substantially identical to each roller coupled to the backing plate.

lo The wedge member may be "V"-shaped. The wedge member may have two "V''shaped portions linked together.

According to a second aspect of the invention there is provided a method for braking a moveable wheel of a motor 15 vehicle, the method comprising the steps of providing a rotor, coupling the rotor to the wheel, providing a caliper to support a backing plate and at least one brake pad, coup' ing the at least one brake pad to the backing plate, providing at least one wedge coupling the or a first of the 20 wedges to the backing plate, coupling a first motor to the first wedge, causing the first motor to move the first wedge so as to cause the at least one brake pad to frictionally engage the rotor thereby braking the vehicle wheel.

25 The method may further comprise providing a second wedge, movably coupling the second wedge to the first wedge, providing a second motor, coupling the second motor to the second wedge, causing the first motor to move the first wedge against the second wedge and against the brake pad 30 effective to cause the at least one brake pad to frictionally engage the rotor thereby braking the vehicle wheel. The first and second motors may be substantially 35 identical.

The first and the second wedges may be dissimilar.

( 9 _ The method may further comprise the steps of providing a selectively repressible braking member, providing a controller and coupling the controller to the or each motor.

The method may further comprise the step of activating the or each motor only when the controller senses a depression of the selectively depressible braking member effective to cause braking of the vehicle wheel.

The method may further comprise the step of sensing a rate of deceleration of the vehicle and communicating the rate of deceleration to the controller.

There may be first and second motors coupled to first and second wedges and the method may further comprise the step of activating the second motor only when the controller senses a depression of the braking member and the sensed rate of deceleration is of a certain value.

The present invention overcomes the drawbacks associated with the prior art in a new and novel fashion by

allowing for a controllably varying amount of self 25 energisation to occur as the amount of friction between the rotor and the pad varies.

It is an advantage of the present invention to provide a method for braking a selectively movable assembly which 30 overcomes some or all of the drawbacks associated with prior braking methods.

The invention will now be described by way of example with reference to the accompanying drawing of which: Figure 1 is a perspective and partially cut away view of an electromechanical braking assembly which is made in

( o accordance with the teachings of the preferred embodiment of the invention; Figure 2 is a block diagram of the electromechanical 5 braking assembly which is shown in Figure 1; Figure 3 is a block diagram of an electromechanical braking assembly which is made in accordance with a second embodiment of the invention; and 1C Figure 4 is a block diagram of an electromechanical braking assembly which is made in accordance with a third embodiment of the invention.

15 Referring now to Figures 1 and 2, there is shown an electromechanical brake assembly 10 which is made in accordance with a first or preferred embodiment of the invention. 20 The electromechanical brake assembly 10 includes at least one rotor 12 which is attached to and which selectively rotates with a wheel or shaft (not shown) of the selectively movable assembly or vehicle (not shown) in which the brake assembly 10 is operatively disposed within.

Further, as shown, the electromechanical brake assembly 10 includes at least one pad member 14 which may selectively engage the movable rotor 12 in a manner which is more fully delineated below and which is effective to brake the 30 selectively movable assembly which operatively contains the electromechanical brake assembly 10. It should be appreciated that multiple pad members 14 may be used within the brake assembly 10 and that a selectively movable assembly, such as a vehicle, may have one brake assembly 10 35 operatively disposed on each selectively movable vehicular wheel.

( Further, the electromechanical brake assembly 10 includes a backing plate 16 which is physically connected or coupled to the pad member 14, a caliper assembly 18 which is coupled to the body or frame 20 of the selectively movable 5 assembly which operatively contains assembly 10, a member 22, such as a pin, bearing, dowel or slide, which is physically connected or coupled to the caliper 18 (e.g., by use of a welded or other conventional connection), a first self energisation member or wedge member 24 having at least lo one wedge or wedge portion 25 and which is physically connected or coupled to the backing plate 16, a second self energisation member or wedge member 26 which has at least one wedge or wedge portion 27 which is selectively and engageably received by the first wedge portion 25, a first motor 30 which includes an output shaft 35 which selectively engages the first wedge member 24, a second motor 34 having an output shaft 36 which selectively engages the second wedge member 26, a computer controller 40 which is operable under stored program control and which is physically, 20 communicatively, and controllably coupled to the first and second motors 30, 34 by the use of respective busses 44, 46, and a source of electrical power 50 such as a battery which is physically coupled to the controller 40 by the use of bus 52. In the preferred embodiment of the invention, caliper 18 "covers" approximately a sixty to ninety degree area of the rotor 12, (i.e., the caliper 18 circumscribes an angle of approximately 60 to 90 degrees of the rotor 12). However, 30 it should be understood to one who is skilled in the relevant art that caliper 18 may be substantially any desired configuration or cover substantially any desired angular portion of rotor 12.

35 The braking assembly 10 further includes an accelerometer 61 which is physically and communicatively coupled to the controller 40 by use of the bus 63. The

f controller 40 is further communicatively coupled to a selectively repressible brake member or pedal 41 by the use of bus 43. The controller 40 and motors 30, 34 may comprise a "controller assembly" and, in one nonlimiting embodiment, 5 motors 30, 34 are substantially identical.

In operation, the brake member 41 is depressed by an operator of the selectively movable assembly when the operator desires to decelerate or brake the selectively JO movable assembly. Upon the detection of the depression of the brake member 41, the controller 40 determines that a certain amount of braking is desired. That is, in one non-

limiting embodiment, a calibrated table having several brake member positions and respective amounts of braking are 5 stored within the controller 40. A braking value is selected by use of the table (e.g., the braking value of the stored brake position which is closest to the currently sensed position is selected from the stored table). The controller 40 then activates the motor 30, thereby causing the shaft 35 20 to engage wedge member 24, effective to force the at least one wedge portion 25 against the at least one wedge portion 27 of the member 26 and this forces the at least one wedge member 26 against frame mounted caliper 18 through member 22 and causes a braking force to be executed on the brake pad 2s 14 by the member 24, effective to initially supply a certain and relatively small amount of braking to the selectively movable assembly which operatively contains assembly 10.

The accelerometer 61 then senses the rate of 30 deceleration of the selectively movable assembly that the brake assembly 10 is operatively disposed within and uses this sensed rate of deceleration to determine the amount of friction which is present or which currently exists between the brake pad 14 and the rotor 12. This determination is 35 achieved in the manner which is more fully discussed below.

The at least one wedge portion 27 of member 26 has an angle of inclination 62 while the at least one wedge portion 25 of member 24 has an angle of inclination 60. Once the member 24 is initially moved in response to the initial 5 sensing of the depression of member 41, a wedge or self energisation angle "a" may be calculated by use of the following equation: 10 Tan() = spun forceps, +, (Equation (output force) where: "a" = coefficient of friction between the brake pad 14 and the rotor 12; "output force" = frictional force acting on the rotor 12 and "input force" = force provided by motor 30 acting on the wedge member 24 which may be sensed (e.g., by use of a force sensor which is coupled to the motor 30) or easily measured by the controller 40.

20 The "output force" may be calculated by the controller 40 as a front output force and a rear output force as follows: output force (front) - 0. 5*F x b x Rt/RC (Equation 2) output force (rear)= 0.5*F x(1-b)x R:/RC (Equation 3) where: "F" = the decelerative force which is measured 30 by the accelerometer 61; "Rt" is the radius of the Lyre which is attached to the wheel upon which brake assembly 10 is operatively disposed (not shown) and which may be easily measured; "RC" is the effective radius of the caliper 18 which may be easily measured and "b" is the percentage of 35 total braking force which is supplied by the front tires and which may be measured or sensed by the controller 40.

( - 14 Hence, by knowing the initial angle "a", which may be determined by the controller 40 by idenT.ifyiT.s the wedge member which is initially moved (e.s., the variable "a" is equal to the va'ue of angle 60 when wedge 24 is moved), the 5 value of "I" may be easily determined by the controller 4C.

Thus, the amount of friction between the brake pad 14 and rotor 12 may then be ascertained by the controller 40.

Particularly, in high friction conditions, the second lo motor 34 is not activated and the wedge member 26 is substantially stationary. The first motor 30 continues to be activated by the controller 40, effective to cause the output shaft 35 to move the wedge member 24 and causing the wedge portion 25 of member 24 to engage the member 26 (to l5 engage portion 27), thereby providing self energisation since the angle 60 of the wedge portion 25 of the wedge member 24 causes or forces the wedge portion 27 of the wedge member 26 to engage member 22 and causes member 24 to provide force onto the brake pad 14. It should be realized 20 that the first motor 30 is activated upon receipt of electrical power which is sourced from the power supply 50 and communicated to the first motor 30 by the use of busses 52, and 44. Alternatively, motors 30, 34 may both be activated in order to actuate the wedge members 24, 26 in 25 opposite directions, thereby providing both force upon the brake pad 14 and self energisation in substantially high friction environments.

In relatively low friction environments associated with 30 a certain rate of deceleration which are sensed by the controller 40 in the foregoing manner or conditions, both of the motors 30 and 34 are activated, thereby causing the output shafts 35 and 36 to move wedge members 24, 26 in substantially the same direction, thereby providing an 35 overall lower angle of inclination (e.g., the effective angle of inclination is relatively small and is equal to the difference between angle 60 and 62).

( In the forgoing manner, the electromechanical brake assembly 10 provides a controllably varying amount of self energisation effective to allow the brake assembly 10 to 5 always provide a substantially large amount of self energisation even under varying environmental conditions.

Thus motors 30, 34 may each be relatively small and cooperatively provide a redundant braking architecture, since the braking assembly 10 may operate with only one of lo the motors 30, 34. In one non-limiting embodiment, the foregoing frictional measurements and calculations may be periodically accomplished by the controller 40 as the brake assembly lo is being operated and, based upon these calculations, the controller 40 may dynamically control 5 motors 30, 34 to dynamically vary the amount of provided self energisation in a controlled manner.

In yet another non-limiting embodiment of the invention, an intermediate gear assembly, such as gear 20 assembly 38, may be coupled to either/both of the output shafts 35, 36, and a screw actuator assembly, such as screw actuator assembly 39, is coupled to each assembly 38. As shown in Figure 2, a pair of assemblies 38, 39 cooperatively transfers energy from a shaft 35, 36 to a member 24, 26. It 25 should be understood that many different actuation means or devices may be employed to actuate the wedge members 24, 26 and that nothing in this description is meant to limit the

present assembly 10 to include the assemblies 38, 39.

30 Referring now to Figure 3, there is shown a brake assembly 100 which is made in accordance with a second embodiment of the invention. Particularly, brake assembly 100 differs from brake assembly 10 in that wedge members 24 and 26 are replaced by a single "V"-shaped wedge 102, the member 22 is replaced with a roller member 104 contacting the upper surface of wedge 102, and two substantially identical roller members 106 are attached to the backing

( - 16 plate 16 and protrude from the baking plate 16 in a direction toward the wedge member 102 to contact the lower surface of wedge 102.

5 As shown in Figure 3, the upper and lower surfaces of wedge 102 are at different angles and the movement of the pad 14, backing plate 16, and roller 106 by motor 30 selectively forces brake pad 14 against the rotor 12. That is, the bottom wedge angle of wedge member 102 is utilized 1 by motor 30 to provide self energisation in relatively high friction environments. In relatively low friction environments, motors 34, 30 may both be activated to actuate both the wedge member 102 (i.e., by use of motor 34) and the backing plate 16 (i.e., by use of motor 30) in order to move 5 the wedge member 102 in substantially the same direction as the backing plate 16.

Alternatively, in substantially high friction environments, motors 30, 34 may be activated in order to 20 actuate the wedge member 102 in a substantially opposite direction as the backing plate 16. It should be understood that in this first alternate embodiment of the invention, the backing plate 16 is actuated in substantially the same manner as the wedge member 24 of the preferred embodiment.

The use of rollers 104 and 106 reduces friction by eliminating or reducing the amount of friction which typically occurs between the member 22 and the wedge member 24 and by eliminating or reducing the amount of friction 3c which occurs between the wedges members 24, 26. Such reduced friction allows the motors 30, 34 to be even smaller than those used in the embodiment which is shown and described with respect to Figures 1 and 2. In one non-limiting embodiment, roller member 104 may be substantially identical 35 to roller member 106.

( Referring now to Figure 4, there is shown a brake assembly 200 which its made in accordance with a third embodiment of the invention and which differs from the brake assembly 100 in that two rollers 202, 204 are usedinstead 5 of the single roller 104 and four rollers 06, 208, 210, and 212 are used instead of the rollers 106. The use of these rollers 206-212 not only reduces friction but ensures that the pad 14 remains substantially parallel to the rotor 12, thereby eliminating taper wear.

It is to be understood that the invention is not limited to the exact construction which has been delineated above, but that various changes and modifications may be made without departing from the scope of the invention.

Claims

( - 18 Claims

1. A brake assembly for braking a selectively moveable assembly the brake assembly having at least one 5 movable self energisation member and a controller assembly coupled to the or each movable se' f energisation member and which is operable to provide a controllable varying amount of self energisation.

1C

2. A brake assembly as claimed in claim 1 in which there is a pair of movable self energisation members each of which has a respective unique angle of inclination and the controller assembly is coupled to the pair of selectively movable members and arranged to cause the pair of movable i self energisation members to cooperative so as to provide a controllable varying amount of self energisation.

3. A brake assembly as claimed in claim 2 further comprising an accelerometer which is coupled to the 20 controller assembly and which generates a certain signal which is transmitted to the controller assembly and which causes the controller assembly to move at least one of the pair of selectively movable members by a certain amount.

25

4. A brake assembly as claimed in claim or in claim 3 wherein each of the movable self energisation members has at least one wedge portion.

5. A brake assembly as claimed in any of claims 2 to 30 4 wherein a first of the pair of selectively movable members has a wedge portion which is dissimilar from a wedge portion of a second of the pair of selectively movable members.

6. A brake assembly as claimed in any of claims 2 to 35 5 wherein the controller assembly comprises an electronic controller which is operable under stored program control, a first motor which selectively moves one of the pair of self

( 1 9 energisation members and which is coupled to the electronic controller and a second motor which selectively moves a second of the pair of self energisation members and which is coupled to the electronic controller.

s

7. A brake assembly as claimed in claim 6 wherein the first and second motors are substantially identical.

8. A brake assembly as claimed in any of claims 2 to lC 7 wherein a wedge portion of the first of the pair of self energisation members frictionally and slidably engages with a wedge portion of a second of the pair of self energisation members. 15

9. A brake assembly as claimed in any of claims 2 to 8 wherein a brake pad is coupled to a first one of the pair of self energisation members.

10. A brake assembly as claimed in claim 1 in which 2 there is one self energisation member and the controller assembly comprises a brake pad for frictional engagement with a movable rotor, a backing plate which is coupled to the brake pad, at least one roller which is coupled to the backing plate, a caliper having at least one roller coupled 25 thereto wherein the self energisation member is a wedge member positioned between the or each roller coupled to the backing plate and the or each roller coupled to the caliper and is coupled to a motor used to selectively move the wedge member so as to brake a selectively movable assembly.

11. A brake assembly as claimed in claim 10 wherein the or each roller coupled to the caliper orthogonally projects therefrom.

35

12. A brake assembly as claimed in claim 10 or in claim 11 wherein the or each roller coupled to the backing plate orthogonally projects therefrom.

(

13. A brake assembly as claimed in ar.y of claims 1C to 12 wherein each roller coupled to the caliper is substantially identical to each roller coupled to the 5 backing plate.

14. A brake assembly as claimed in any of claims 10 to 13 wherein the wedge member is "V"-shaped.

lo

15. A method for braking a moveable wheel of a motor vehicle, the method comprising the steps of providing a rotor, coupling the rotor to the wheel, providing a caliper to support a backing plate and at least one brake pad, coupling the at least one brake pad to the backing plate, 75 providing at least one wedge coupling the or a first of the I wedges to the backing plate, coupling a first motor to the I first wedge, causing the first motor to move the first wedge so as to cause the at least one brake pad to frictionally engage the rotor thereby braking the vehicle wheel. i 2c

16. A method as claimed in claim 15 wherein the method further comprises providing a second wedge, movably coupling the second wedge to the first wedge, providing a second motor, coupling the second motor to the second wedge, 25 causing the first motor to move the first wedge against the second wedge and against the brake pad effective to cause I the at least one brake pad to frictionally engage the rotor thereby braking the vehicle wheel.

30

17. A method as claimed in claim 16 wherein the first and second motors are substantially identical.

18. A method as claimed in claim 16 or in claim 17 wherein the first and the second wedges are dissimilar.

19. A method as claimed in any of claims 15 to 18 wherein the method further comprises the steps of providing

! - 21 a selectively Repressible braking member, providing a control 'er and coupling the controller to the or each motor.

20. A method as claimed in claim l9 further comprising 5 the step of activating the or each motor only when the controller senses a depression of the selectively Repressible braking member effective to cause braking of the vehicle wheel.

is

21. A method as claimed in claim 19 or in claim 20 further comprising the step of sensing a rate of deceleration of the vehicle and communicating the rate of deceleration to the controller.

15

22. The method as claimed in claim 20 or in claim 21 1 when dependent upon claim 20 in which there are first and second motors coupled to first and second wedges and the method further comprises the step of activating the second motor only when the controller senses a depression of the 20 braking member and the sensed rate of deceleration is of a certain value.

23. A braking assembly substantially as described herein with reference to the accompanying drawing.

24. A method for braking a moveable wheel of a motor I vehicle substantially as described herein with reference to the accompanying drawing.